Electrocaloric effect heat transfer device dimensional stress control

ABSTRACT

Technologies are generally described herein for electrocaloric effect heat transfer devices and methods effective to facilitate thermal energy transfer while mitigating mechanical stresses caused by expansion or contraction of electrocaloric effect material layers during thermal energy transfer operations. Some example heat transfer devices may include heat transfer stacks with at least two electrocaloric effect materials. Expanding electrocaloric effect material and contracting electrocaloric effect material are utilized to cancel the aggregate longitudinal dimensional change during application of an electric field. Some example heat transfer devices may utilize segmented electrocaloric effect material layers with stress relief gaps separating segments to mitigate delamination stress caused by lateral expansion or contraction of the electrocaloric effect material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application under 35 U.S.C. §121 of andclaims priority under 35 U.S.C. §120 to co-pending U.S. National Stagefiling, application Ser. No. 13/386,736 filed on Jan. 24, 2012 nowissued as U.S. Pat. No. 8,739,553, which in turn is a national stagefiling under 35 U.S.C. §371 of PCT application serial numberPCT/US2011/052569, entitled, “Electrocaloric Effect Heat Transfer DeviceDimensional Stress Control,” filed Sep. 21, 2011. This application isrelated to co-pending application serial number PCT/US2010/039200,entitled, “Electrocaloric Effect Materials and Thermal Diodes,” filed onJun. 18, 2010, corresponding U.S. National Stage filing, applicationSer. No. 12/999,684, entitled “Electrocaloric Effect Materials andThermal Diodes,” filed on Dec. 17, 2010, and is related to co-pendingapplication serial number PCT/US2011/033220, entitled, “HeterogeneousElectrocaloric Effect Heat Transfer Device,” filed on Apr. 20, 2011,each of which is herein incorporated by reference in their entirety.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Electrocaloric effect materials are materials that can experience atemperature change when subjected to an applied electric field. Thistemperature change can be reversed upon the removal of the appliedelectric field. By physically coupling and decoupling electrocaloriceffect material to and from a heat source, thermal energy can bedynamically transferred in quantities that are greater in one directionthan the other. The described principles may be applied to a heattransfer device that can be utilized to transfer thermal energy awayfrom a heat source.

The present disclosure appreciates that the electrocaloric effect andother materials used in various types of heat transfer devices mayexperience dimensional changes with the application and removal of theapplied electric field. As a result, the volume of the electrocaloriceffect material layers may undesirably change in the longitudinaldirection of the thermal energy flow during operation of the heattransfer device, creating a cumulative strain that may result inundesirable bending, which may decouple the material from the heatsource, decouple the material from the heat dump, or may result in someother mechanical problem or failure. Moreover, because of the lateraldimensional change of the electrocaloric effect material layers in aheat transfer device, these layers may experience a delamination stressthat is cyclical with the application and removal of the appliedelectric field. The cyclic delamination stress may result indelamination with adjacent material layers, potentially leading toreliability issues.

SUMMARY

The present disclosure generally describes techniques for electrocaloriceffect heat transfer devices and methods that may be effective tofacilitate thermal energy transfer over a wide operating temperaturerange of a corresponding heat source. According to some exampleembodiments, a heat transfer device may include multiple electrocaloriceffect materials. A first electrocaloric effect material may beconfigured to expand and to change temperature when an electric field isapplied. A second electrocaloric effect material may be configured tocontract and to change temperature when the electric field is applied. Athermal rectifier material may be configured in thermal contact with theelectrocaloric effect materials, facilitating thermal energy transfermore readily in one direction than the other.

The present disclosure also generally describes methods that may beemployed for transferring thermal energy from a heat source to a heatdump. Some example methods may include applying an electric field acrossan expanding electrocaloric effect material layer and across acontracting electrocaloric effect material layer of a heat transferdevice that is configured in thermal contact with the heat source andthe heat dump. During the application of the electric field, thermalenergy can be transferred from the heat source to a heat dump throughthe expanding and contracting electrocaloric effect material layerswhile maintaining an approximate total length of the heat transferdevice.

The present disclosure further generally describes a heat transferdevice that may include a number of electrocaloric effect materiallayers and thermal rectifier material layers positioned between theelectrocaloric effect material layers. The electrocaloric effectmaterial layers may include at least one segmented expandingelectrocaloric effect material layer and at least one segmentedcontracting electrocaloric effect material layer. The segmentedexpanding electrocaloric effect material layer can be configured toexpand a longitudinal expansion distance when subjected to an electricfield, while the segmented contracting electrocaloric effect materiallayer can be configured to contract a longitudinal contraction distancethat is approximately equal to the longitudinal expansion distance whensubjected to the electric field.

The present disclosure additionally generally describes a heat transferdevice that may include first and second electrocaloric effect materialsand a thermal rectifier material configured in thermal contact with eachof the electrocaloric effect materials. Each electrocaloric effectmaterial may be configured with a number of electrocaloric effectmaterial segments separated by a number of stress relief gaps. Thethermal rectifier material can be configured to facilitate thermalenergy transfer between electrocaloric effect materials in one directionand to limit thermal energy transfer in the opposite direction.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other features of this disclosure will become morefully apparent from the following description and appended claims, takenin conjunction with the accompanying drawings. Understanding that thesedrawings depict only several embodiments in accordance with thedisclosure and are, therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings, in which:

FIG. 1 is a functional block diagram illustrating an exampleelectrocaloric effect heat transfer system with correspondingelectrocaloric effect heat transfer device;

FIG. 2 is a perspective view of an example heat transfer stack of anelectrocaloric effect heat transfer system;

FIG. 3 is a cross-sectional view of an example electrocaloric effectheat transfer device taken along line A-A of FIG. 1 illustratinglongitudinal stress within the heat transfer stack caused by a change ina longitudinal dimension of the heat transfer stack during operation;

FIG. 4 is a cross-sectional view of an example electrocaloric effectheat transfer device taken along line A-A of FIG. 1 illustrating a heattransfer stack configured with heterogeneous electrocaloric effectmaterial layers;

FIG. 5 is a cross-sectional view of an example electrocaloric effectheat transfer device taken along line A-A of FIG. 1 illustrating analternative configuration of a heat transfer stack configured withheterogeneous electrocaloric effect material layers;

FIG. 6 is a cross-sectional view of an example electrocaloric effectheat transfer device taken along line A-A of FIG. 1 illustrating yetanother alternative configuration of a heat transfer stack configuredwith heterogeneous electrocaloric effect material layers;

FIG. 7 is a cross-sectional view of an example electrocaloric effectheat transfer device taken along line A-A of FIG. 1 illustrating lateralstress within the heat transfer stack caused by a change in a lateraldimension of the heat transfer stack during operation;

FIG. 8 is a perspective view of an example heat transfer stack of anelectrocaloric effect heat transfer system having stress relief gapsincorporated within electrocaloric effect material layers;

FIG. 9 is a top view of the example heat transfer stack of FIG. 8;

FIG. 10 is a flow diagram illustrating an example process forimplementing an electrocaloric effect heat transfer device to reducestress induced by dimensional changes of electrocaloric effect materialduring application of an electric field; and

FIG. 11 is a block diagram illustrating a computer hardware architecturecorresponding to an example controller, all arranged in accordance withat least some embodiments described herein.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented herein. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe Figures, can be arranged, substituted, combined, separated, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated herein.

This disclosure is generally drawn, inter alia, to electrocaloric effectheat transfer techniques that control the mechanical stresses induced bydimensional changes of electrocaloric effect material layers duringoperation of a heat transfer device. In an illustrative implementation,an electrocaloric effect heat transfer device may be configured withmultiple electrocaloric effect materials having longitudinal dimensionalchanges that approximately cancel one another during operation tominimize or approximately eliminate a longitudinal increase or decreasein length of a heat transfer stack while transferring thermal energybetween a heat source and a heat dump. Each electrocaloric effectmaterial layer of a heat transfer stack may be additionally oralternatively configured with any number of electrocaloric effectmaterial segments having stress relief gaps between the segments. Thestress relief gaps may allow for the absorption of lateral dimensionalchanges in the electrocaloric effect material so as to reduce orapproximately eliminate the delamination stress within theelectrocaloric effect material layer during operation of the heattransfer device.

FIG. 1 is a functional block diagram illustrating an exampleelectrocaloric effect heat transfer system 100 with correspondingelectrocaloric effect heat transfer device 102. The electrocaloriceffect heat transfer device 102 includes one or more heat transferstacks 104A-104N, arranged in accordance with at least some embodimentsdescribed herein. Heat transfer stacks 104A-104N may collectively bereferred to as “104” and will be described in detail below with respectto FIGS. 2-9.

One surface 116 of the electrocaloric effect heat transfer device 102can be thermally coupled to a heat source 106 to be cooled. An opposingsurface 118 of the electrocaloric effect heat transfer device 102 can bethermally coupled to a heat dump 108, which receives thermal energytransferred from the heat source 106 by the electrocaloric effect heattransfer device 102. The thermal coupling may include directsurface-to-surface contact between the electrocaloric effect heattransfer device 102 and the heat source 106, as well as between theelectrocaloric effect heat transfer device 102 and the heat dump 108,with or without a physical connection or coupling of the components.Alternatively, additional intervening components may be utilized tothermally couple the electrocaloric effect heat transfer device 102 tothe heat source 106 and to the heat dump 108, provided that theintervening components provide a thermally conductive path thatfacilitates thermal energy transfer between the components of theelectrocaloric effect heat transfer system 100. Other exampleintervening components may include, but are not limited to, thermalgrease or paste, thermally conductive adhesives and adhesive tapes,thermally conductive shims, and solder.

The electrocaloric effect heat transfer device 102 can be electricallycoupled to a power source 110 via one or more electrodes 114. It shouldbe appreciated that although the electrodes 114 are represented in FIG.1 as a single box or rectangle, implementations may include any numberand type of electrodes 114 positioned appropriately throughout theelectrocaloric effect heat transfer device 102, where the electrodes areoperable to subject the various electrocaloric effect material layers ofthe heat transfer stacks 104 to electrical fields provided by the powersource 110. For example, as will be described in further detail belowwith respect to FIG. 2, each heat transfer stack 104 includesalternating layers of electrocaloric effect material and thermalrectifier material.

According to some implementations, two electrodes 114 may be positionedon opposing sides of the electrocaloric effect material layer,optionally encompassing an adjacent thermal rectifier material layer.Example electrodes 114 are further described and illustrated inapplication serial number PCT/US2010/039200, entitled, “ElectrocaloricEffect Materials and Thermal Diodes,” filed on Jun. 18, 2010, andcorresponding U.S. National Phase filing, U.S. application Ser. No.12/999,684, entitled “Electrocaloric Effect Materials and ThermalDiodes,” filed on Dec. 17, 2010, each of which is herein incorporated byreference in its entirety.

In some examples, an electrode control signal may be applied to theelectrodes 114 from the power source 110 effective to generate anelectric field across the associated electrocaloric effect material. Thesame or like electrode control signal may be applied substantiallysimultaneously to the electrodes 114 of every other electrocaloriceffect material layer within a heat transfer stack 104. As every secondlayer of electrocaloric effect material within a heat transfer stack 104is subjected to an electric field to produce a cold phase, theintervening layers of electrocaloric effect material are not subjectedto an electric field, which creates a hot phase in those layers. As theelectrode control signal is cyclically applied to the alternating layersof electrocaloric effect material, thermal energy is transferred fromthe hot phase layers to the cold phase layers in a direction from theheat source 106 to the heat dump 108.

The electrode control signal may be any type of signal that is effectiveto produce the desired temperature change within the electrocaloriceffect material and corresponding heat transferring action that mayfacilitate transfer of thermal energy away from the heat source 106.According to some implementations, the electrode control signal may bean oscillating signal such as a voltage or current. The oscillatingsignal may be provided as any of a variety of signal waveforms. In someexamples, the oscillating signal may be provided as a pulsed signal witha direct current (DC) voltage or DC current of a specified amplitudethat is pulsed on or off (or simply between an upper voltage and lowervoltage) with a specified duty cycle and period. In some additionalexamples, the oscillating signal may be provided as a sinusoidal signalwith an alternating current (AC) voltage or AC current of a specifiedamplitude, frequency, phase and DC offset. In still additional examples,the oscillating signal may be provided as a ramped or sawtooth signalwith a specified amplitude, rate, period and DC offset. In still otherexamples, the oscillating signal may be provided as a triangular signalwith a specified amplitude, first ramp rate (e.g., increasing), secondramp rate (e.g., decreasing), period, and DC offset. Additionalwaveforms or combinations of waveforms are also contemplated.

The electrocaloric effect heat transfer system 100 may include acontroller 112 that is configured to operatively control the electrodecontrol signal or signals applied to the electrodes 114 from the powersource 110 to create the desired electric fields that drive the transferof thermal energy through the system. The controller 112 may beconfigured to operatively control the application of the electrodecontrol signal according to an operating temperature of the heat source116, as detected with a temperature sensor 120 that may becommunicatively coupled to the controller 112. Embodiments of thepresent disclosure may be implemented within a number of heat transferstacks 104, with varying electrocaloric effect material 202 compositionamong and between the heat transfer stacks 104 to efficiently transferthermal energy over a wide operating temperature range, as described indetail and illustrated in application serial number PCT/US2011/033220,entitled, “Heterogeneous Electrocaloric Effect Heat Transfer Device,”filed on Apr. 20, 2011, which is herein incorporated by reference in itsentirety.

The controller 112 may include any type of computer hardware and/orsoftware capable of providing the electrode control signal at thedesired waveform characteristics according to, inter alia, theelectrocaloric effect material used. The controller 112 may be includedas part of the electrocaloric effect heat transfer device 102, or may bean external component of the electrocaloric effect heat transfer system100 as shown in FIG. 1. The controller 112, as arranged in accordancewith at least some embodiments will be described in greater detail belowwith respect to FIG. 11.

It should be appreciated that the heat source 106 may be any electroniccomponent, computer component, appliance, or any device that maygenerate or absorb thermal energy during operation. Similarly, the heatdump 108 may include any thermally conductive material such as a metalor metal alloy heat sink material. In some examples, the heat dump 108may be comprised of a computer case or an electronics case that isthermally conductive material capable of receiving thermal energy fromthe electrocaloric effect heat transfer device 102 at any operatingtemperature of the heat source 106. Alternatively, rather than includinga metal or other solid material, the heat dump 108 may include gas orliquid. In some implementations, the heat dump 108 may include bothconductive material and liquid or gas such as a heat pipe apparatuswhere the inside of the heat pipe may be comprised of liquid/gas and theexterior of the heat pipe may be a metal alloy. Additional combinationsof thermally conductive materials, liquids and gases are contemplated.Example thermally conductive materials may include, but are not limitedto, aluminum, copper, silver, gold, platinum, tungsten, and other metalor metal alloys. Although less thermally conductive than the metal andmetal alloys described above, other materials that are suitable for hightemperatures, such as ceramics, are also contemplated. Example gasessuitable for the present application may include air, nitrogen, helium,and other gases. Noncorrosive gases may be suitable for the presentapplication, including multi-component gas mixtures such as aHelium-Xenon mixture. Example liquids suitable for the presentapplication gases include water, liquid nitrogen, liquid helium,ethylene glycol, alcohol, and ionic liquids.

FIG. 2 is a perspective view of an example heat transfer stack 104 of anelectrocaloric effect heat transfer system 100, arranged in accordancewith at least some embodiments described herein. The heat transfer stack104 may be thermally coupled to a heat source 106. According to thisexample, the heat transfer stack 104 may include alternating layers ofelectrocaloric effect material 202 and thermal rectifier material 204. Alayer of thermal rectifier material 204 may be positioned between theheat source 106 and the first layer of electrocaloric effect material202 and configured such that a first surface of the thermal rectifiermaterial 204 abuts a surface of the heat source 106, and an opposingsecond surface of the thermal rectifier material 204 abuts a surface ofthe first layer of electrocaloric effect material 202. In this manner,the first layer of electrocaloric effect material 202 can be configuredin indirect thermal contact with the heat source 106 and direct thermalcontact with the thermal rectifier material 204. Alternatively, itshould be appreciated that any thermally conductive compound mayintervene between the first layer of electrocaloric effect material 202and the heat source 106, between the first layer of thermal rectifiermaterial 204 and the heat source 106, or between the first layer ofthermal rectifier material 204 and the first layer of electrocaloriceffect material 202. Examples include, but are not limited to, a silvergel compound, copper plate, thermal grease or paste, thermallyconductive adhesives and adhesive tapes, solder, and/or any type ofthermally conductive shim. As an oscillating voltage or other electrodecontrol signal can be supplied to the electrodes 114 coupled to thelayers of electrocaloric effect material 202, a resulting electric fieldbiases the electrocaloric effect material to facilitate the transfer ofthermal energy away from the heat source 106 and through the layers ofthe heat transfer stack 104.

According to various implementations described herein, each heattransfer stack 104 may include at least two layers of electrocaloriceffect material 202, utilizing at least two types of electrocaloriceffect materials 202. As will be described in greater detail below withrespect to FIGS. 3-6, the types of electrocaloric effect materials for aheat transfer stack 104 may be selected such that the total longitudinalexpansion of electrocaloric effect material is substantially equivalentto the total longitudinal contraction of electrocaloric effect materialwhen subjected to applied electric fields. In doing so, the totallongitudinal dimensional change of the heat transfer stack 104 issubstantially eliminated or minimized during operation, which reducesthe mechanical stresses associated with expansion or contraction of aconventional heat transfer device 102.

The thermal rectifier material 204, which can also be referred to as athermal diode, may have an asymmetrical thermal conductancecharacteristic where thermal energy may be transported more readily inone general direction than in another, as indicated by the open arrow inFIG. 2. Another way of stating the thermal energy transfercharacteristic of the thermal rectifier material 204 is that the thermalrectifier material 204 may be configured to resist thermal energytransfer in a direction from the heat dump 108 to the heat source 106after removal of the electric field from the corresponding heat transferstack 104. Although for clarity purposes, each layer of the thermalrectifier material 204 is illustrated as a uniform sheet, it should beappreciated that according to various implementations, the thermalrectifier material 204 may include any quantity of uniform ornon-uniform sheets of suitable materials having different temperaturecoefficients of thermal conductivity. The materials having differenttemperature coefficients of thermal conductivity may be configured inthermal contact with one another, or may utilize heat pipes, actuators,or any other implementation that can be adapted to allow thermal energyto more readily flow in one direction than the other. Moreover, thethermal rectifier material 204 characteristics may be substantiallyhomogeneous throughout the various layers of a single heat transferstack 104 in that each thermal rectifier material layer may include thesame characteristics as other thermal rectifier material layers,including but not limited to the type of thermal rectifier material, aswell as the layer dimensions and shape. Alternatively, the thermalrectifier material 204 layers may differ in any characteristics within asingle heat transfer stack 104.

The precise characteristics of a single heat transfer stack 104 may varyaccording to the desired heat transfer performance for the particularimplementation. For example, the electrocaloric effect material 202, thematerials used within the thermal rectifier material 204, thepositioning of the electrodes 114 and corresponding voltage application,and the method of creating a heat transfer stack 104 and associatedlayers may vary according to any number and type of heat transferperformance criteria associated with the particular implementation.These heat transfer stack characteristics and others are described inapplication serial number PCT/US2010/039200, entitled, “ElectrocaloricEffect Materials and Thermal Diodes,” filed on Jun. 18, 2010, andcorresponding U.S. National Phase filing, U.S. application Ser. No.12/999,684, entitled “Electrocaloric Effect Materials and ThermalDiodes,” filed on Dec. 17, 2010, each of which is herein incorporated byreference in its entirety.

FIG. 3 is a cross-sectional view of an example electrocaloric effectheat transfer device 102 taken along line A-A of FIG. 1 illustratinglongitudinal stress 310 within the heat transfer stack 104 caused by achange in a longitudinal dimension of the heat transfer stack 104 duringoperation. As discussed above, due to the characteristics of variouselectrocaloric effect materials 202, an electric field applied to anelectrocaloric effect material 202 produces a desired temperature changewithin the electrocaloric effect material and corresponding thermalenergy transferring action that facilitates transfer of thermal energyaway from the heat source 106, and also may produce a change in thevolume of the electrocaloric effect material. A longitudinal dimensionalchange can be described as being an expansion or contraction along alongitudinal axis 304. An undesirable effect of this longitudinaldimensional change may arise when the one or more heat transfer stack104 is coupled to the heat source 106 and the heat dump 108, which maybe rigidly positioned a fixed distance 308 from one another as measuredalong the longitudinal axis 304.

As illustrated in this example by the expansion arrows 302, someelectrocaloric effect materials 202 may expand when subjected to anelectric field. When a heat transfer stack 104 is homogeneous withrespect to the electrocaloric effect material layers such that onlyexpanding electrocaloric effect materials 202 are used throughout theheat transfer stack 104, the expansion results in an unconstrainedlongitudinal length 306 of the heat transfer stack 104 that may begreater than the fixed distance 308 between the heat source 106 and theheat dump 108, which may create a longitudinal stress 310. An oppositebut similarly undesirable effect may occur when a heat transfer stack104 is homogeneous with respect to the electrocaloric effect materiallayers such that contracting electrocaloric effect materials 202 areused throughout the heat transfer stack 104. In this contractingexample, the unconstrained longitudinal length 306 of the heat transferstack 104 may be less than the fixed distance 308 between the heatsource 106 and the heat dump 108, which may cause detachment ordelamination between layers of the heat transfer stack 104 or betweenthe heat transfer stack 104 and the heat source 106 or heat dump 108.For the purposes of this disclosure, the unconstrained longitudinallength 306 may be the dimension of the heat transfer stack 104 along thelongitudinal axis 304 if the heat transfer stack were not coupled to theheat source 106 and heat dump 108 so that the heat transfer stack isfree to expand to a maximum length or contract to a minimum length.

To eliminate or mitigate the longitudinal stress 310 caused by utilizingheat transfer stacks 104 with homogeneous electrocaloric effect materiallayers, some embodiments provided herein may utilize heat transferstacks 104 having heterogeneous electrocaloric effect material layers.According to some of the various embodiments, a heat transfer stack 104having heterogeneous electrocaloric effect material layers may have atleast two types of electrocaloric effect materials 202, creating atleast two types of electrocaloric effect material layers within the heattransfer stack 104. At least one type of electrocaloric effect material202 may be an expanding material such that the electrocaloric effectmaterial 202 expands a first longitudinal distance along thelongitudinal axis 304 when subjected to an electric field. An example ofa suitable expanding electrocaloric effect material 202 includes PZT,which is also known as lead zirconate titanate (Pb[Zr_(x)Ti_(1-x)]O₃0≦x≦1), although it should be appreciated that any electrocaloric effectmaterial 202 that expands with exposure to an electric field may beutilized with the various embodiments disclosed herein.

At least one other type of electrocaloric effect material 202 within aheat transfer stack 104 having heterogeneous electrocaloric effectmaterial layers may be a contracting type of material such that theelectrocaloric effect material 202 contracts a second longitudinaldistance along the longitudinal axis 304 when subjected to the electricfield. Examples of suitable contracting electrocaloric effect materials202 include, but are not limited to, polyvinylidene fluoride, or PVDF,copolymers such as P(VDF-TrFE) and P(VDF-TrFE-CFRE). Any electrocaloriceffect material 202 that contracts with exposure to an electric fieldmay be utilized with the various embodiments disclosed herein.

As will be discussed in detail below, any number and type ofheterogeneous electrocaloric effect material layers may be utilizedwithin various heat transfer stacks 104 to create a heat transfer stack104 in which the unconstrained longitudinal length 306 is approximatelyequivalent to the fixed distance 308 between the heat source 106 and theheat dump 108. Such an arrangement of heterogeneous materials may cancelthe expansion and contraction effects in the electrocaloric effectmaterial layers. In other words, the aggregate first longitudinaldistance may corresponding to the total expansion distance of theelectrocaloric effect material layers, which may be approximatelyequivalent to the aggregate second longitudinal distance correspondingto the total contraction distance of the electrocaloric effect materiallayers. The longitudinal stress 310 described above with respect to aheat transfer stack 104 having homogeneous electrocaloric effectmaterial layers may be eliminated or substantially mitigated.

FIG. 4 is a cross-sectional view of an example electrocaloric effectheat transfer device 102 taken along line A-A of FIG. 1 illustrating aheat transfer stack 104 configured with heterogeneous electrocaloriceffect material layers. As previously described, the heterogeneouselectrocaloric effect material layers may include expandingelectrocaloric effect material layers 202A and contractingelectrocaloric effect material layers 202B. According to thisembodiment, the expanding electrocaloric effect material layers 202A canbe positioned consecutively adjacent to one another with a layer ofthermal rectifier material 204 disposed between adjacent layers ofexpanding electrocaloric effect material to create an expanding heattransfer portion 402. Similarly, the contracting electrocaloric effectmaterial layers 202B can be positioned consecutively adjacent to oneanother with a layer of thermal rectifier material 204 disposed betweenadjacent layers of contracting electrocaloric effect material to createa contracting heat transfer portion 404. During application of theelectric field, the longitudinal expansion distance of the expandingheat transfer portion 402 along the longitudinal axis 304 mayapproximately equal the longitudinal contraction distance of thecontracting heat transfer portion 404 along the longitudinal axis 304.In this manner, the unconstrained longitudinal length 306 of the heattransfer stack 104 may be approximately equivalent to the fixed distance308 between the heat source 106 and the heat dump 108, effectivelynegating any longitudinal stress 310 or delamination during operation ofthe heat transfer device.

According to some embodiments, the heat transfer stack 104 may includean identical number of expanding electrocaloric effect material layers202A and contracting electrocaloric effect material layers 202B. Theexpanding electrocaloric effect material layers 202A may be grouped andpositioned adjacent to one another at either the heat source side of theheat transfer stack 104, or adjacent to the heat dump side of the heattransfer stack 104. Similarly, the contracting electrocaloric effectmaterial layers 202B may be grouped at one side or the other of the heattransfer stack 104. In this example and others shown and describedherein, the layers of thermal rectifier material 204 may be identicalthroughout the heat transfer stack 104, although it should beappreciated that the thermal rectifier material layers may be similarlyheterogeneous as described herein with respect to the electrocaloriceffect material layers.

The expanding electrocaloric effect material layers 202A shown in FIG. 4are shown to be thinner than the contracting electrocaloric effectmaterial layers 202B. However, it should be appreciated that theexpanding electrocaloric effect material layers 202A and the contractingelectrocaloric effect material layers 202B may be any thickness withrespect to one another. According to some embodiments, the expandingelectrocaloric effect material layers 202A may be thicker than thecontracting electrocaloric effect material layers 202B. According tosome other embodiments, the expanding electrocaloric effect materiallayers 202A and the contracting electrocaloric effect material layers202B may be of substantially equivalent thickness. The precisedimensions of the electrocaloric effect material 202 within the variouslayers may depend on any number of factors, including but not limitedto, the expansion and contraction characteristics of the selectedelectrocaloric effect materials 202, the number of desiredelectrocaloric effect material layers, and the fixed distance 308between the heat source 106 and the heat dump 108. In variousconfigurations, the aggregate longitudinal expansion and contractiondistances of the expanding and contracting electrocaloric effectmaterial layers 202A/202B may be substantially zero during the cold andhot phases of operation of the heat transfer device 102.

FIG. 5 is a cross-sectional view of an example electrocaloric effectheat transfer device 102 taken along line A-A of FIG. 1 illustrating analternative configuration of a heat transfer stack 104 configured withheterogeneous electrocaloric effect material layers. According to thisexample, a heat transfer stack 104 may include alternating groups ofexpanding heat transfer portions 402 and contracting heat transferportions 404. Further embodiments (not shown) may include alternatingsingle expanding and contracting electrocaloric effect material layersrather than grouping like layers, or may include any desired or randomarrangement of layers. The specific groupings and arrangement ofexpanding electrocaloric effect material layers 202A and contractingelectrocaloric effect material layers 202B may depend on any number offactors, including but not limited to, a thickness of the expandingelectrocaloric effect material layers 202A, a thickness of thecontracting electrocaloric effect material layers 202B, a thickness ofeach layer of thermal rectifier material 204, a total length of the heattransfer device or fixed distance 308 between the heat source 106 andthe heat dump 108, an expansion characteristic or attribute of theexpanding electrocaloric effect material, a contraction characteristicor attribute of the second electrocaloric effect material, and thecharacteristics of the electric field to be applied to theelectrocaloric effect material layers. As discussed above, thisdisclosure is not limited to any particular thickness of each layer, orthickness ratio or other relationship between the types ofelectrocaloric effect material layers.

FIG. 6 is a cross-sectional view of an example electrocaloric effectheat transfer device 102 taken along line A-A of FIG. 1 illustrating yetanother alternative configuration of a heat transfer stack 104configured with heterogeneous electrocaloric effect material layers.This example illustrates that the various embodiments are not limited toan equivalent number of expanding electrocaloric effect material layers202A and contracting electrocaloric effect material layers 202B. Anysuitable ratio of expanding to contracting electrocaloric effectmaterial layers may be utilized to effectively cancel the totallongitudinal dimensional change in the heat transfer stack 104 so thatthe unconstrained longitudinal length 306 of the heat transfer stack 104may remain approximately equivalent to the fixed distance 308 betweenthe heat source 106 and the heat dump 108.

Although not specifically illustrated, it should also be appreciatedthat more than two types of electrocaloric effect materials 202 may beutilized within a single heat transfer stack 104 or within adjacent heattransfer stacks 104. For example, multiple expanding electrocaloriceffect materials 202 may be used to create multiple types of expandingelectrocaloric effect material layers 202A, which may be interspersedamong multiple types of contracting electrocaloric effect materiallayers 202B created from multiple contracting electrocaloric effectmaterials 202. For clarity purposes, the various figures illustrate arepresentation for an expanding electrocaloric effect material layer202A and a representation for a contracting electrocaloric effectmaterial layer 202B. Each of these representations may include anynumber and type of corresponding electrocaloric effect materials 202.

FIG. 7 is a cross-sectional view of an example electrocaloric effectheat transfer device 102 taken along line A-A of FIG. 1 illustratinglateral stress 310 within the heat transfer stack 104 caused by a changein a lateral dimension of the heat transfer stack 104 during operation.As previously discussed, an electric field applied to an electrocaloriceffect material 202 may produce a change in the volume of theelectrocaloric effect material. In addition to the longitudinaldimensional change that may be controlled utilizing a heterogeneouselectrocaloric effect material layer configuration described above, anelectrocaloric effect material layer may experience a lateraldimensional change that may create a lateral stress 710 between adjacentlayers of the heat transfer stack 104.

A lateral dimensional change can be described as being an expansion orcontraction along a lateral axis 704. The lateral dimensional change isillustrated in FIG. 7 by the expansion arrows 702, although it should beappreciated that the lateral dimensional change may alternatively be acontraction, such as when utilizing the contracting electrocaloriceffect material layers 202B described above. An undesirable effect ofthis lateral dimensional change is that the lateral stress 710, ordelamination stress, may cause the electrocaloric effect material layersto separate from the adjacent thermal rectifier material layers orotherwise may cause damage to the heat transfer stack 104.

To eliminate or mitigate the lateral stress 710 caused by expansion orcontraction of the electrocaloric effect material layers, theembodiments provided herein may utilize stress relief gaps within theelectrocaloric effect material layers to separate the layers intosegments. The stress relief gaps between the multiple electrocaloriceffect material segments may reduce the accumulation of the delaminatingstress in the plane of the electrocaloric effect material layer.

FIG. 8 is a perspective view of an example heat transfer stack 104 of anelectrocaloric effect heat transfer system 100 having stress relief gaps804 incorporated within electrocaloric effect material layers. FIG. 9 isa top view of the example heat transfer stack 104 of FIG. 8. Looking atthese two figures, it can be seen that the stress relief gaps 804 dividethe electrocaloric effect material 202 into multiple electrocaloriceffect material segments 802A-802N, collectively referred to as “802.”Some embodiments may include a 4×4 array of electrocaloric effectmaterial segments 802, but any number, shape, and configuration ofelectrocaloric effect material segments 802 is contemplated.

According to various implementations, the stress relief gaps 804 can befilled with a gap-filling material having a high electric fieldresistance, but poor adhesion to the electrocaloric effect material 202in order to prevent edge-surface breakdown when a voltage is appliedacross the electrocaloric effect material layer and stress relief gaps804. According to some embodiments, the gap-filling material may behydrogen sulfide gas. According to other embodiments, variousfluorocarbon liquids or electrical greases may be utilized asgap-filling materials. The gap-filling material may have a lower elasticmodulus than the elastic modulus associated with the electrocaloriceffect material 202 to absorb conformational changes of theelectrocaloric effect material 202 without allowing gaps to form betweenthe electrocaloric effect material 202 and the gap-filling material.According to some embodiments, the gap-filling material may have abreakdown voltage per meter that is greater than a voltage per meterapplied to create the electric field. According to other embodiments,the stress relief gaps 804 are left unfilled and the electrocaloriceffect heat transfer device 102 is packaged in an environment thatresists electrical breakdown, such as in a vacuum or within hydrogensulfide gas or other appropriate gas. It should be appreciated that thestress relief gaps 804 are shown in FIGS. 8 and 9 without thegap-filling material for clarity purposes.

The stress relief gaps 804 may be generated in any suitable manner.According to some embodiments, the stress relief gaps 804 can be createdlithographically, or by cutting the material while on a separate elasticcarrier and stretching the carrier before thermal transfer.Alternatively, the stress relief gaps 804 may be cut into theelectrocaloric effect material layers using a tool that removes the cutmaterial, or by a saw having an appropriate kerf.

FIG. 10 is a flow diagram illustrating an example process 1000 forimplementing an electrocaloric effect heat transfer device 102 to reducestress induced by dimensional changes of electrocaloric effect material202 during application of an electric field. The process 1000 mayinclude various operations, functions, or actions as illustrated by oneor more of blocks 1002-1006. It should be appreciated that more or feweroperations may be performed than shown in the FIG. 10 and describedherein. Moreover, these operations may also be performed in a differentorder than those described herein.

The process 1000 may begin at block 1002 (Receive Signal at SegmentedExpanding ECE Material Layers), where one or more electrode controlsignals may be received from the power source 110 at the electrodes 114of the expanding electrocaloric effect material layers 202A of the heattransfer stacks 104. The controller 112 may be configured to control theapplication of this electrode control signal from the power source 110according to an operational status of the heat source 106, a temperatureof the heat source 106, a predetermined schedule, or any other desiredfactor. According to various implementations, the expandingelectrocaloric effect material layers 202A may or may not be configuredas electrocaloric effect material segments 802 having stress relief gaps804 between the segments to accommodate lateral dimensional changes. Asdescribed above, the electrode control signal may include an oscillatingsignal that can be provided as any of a variety of voltage or currentwaveforms to create an electric field to alternately activate anddeactivate the electrocaloric effect material segments 802 of the heattransfer stacks 104. Block 1002 may be performed concurrently with block1004.

At block 1004 (Receive Signal at Segmented Contracting ECE MaterialLayers), where one or more electrode control signals may be receivedfrom the power source 110 at the electrodes 114 of the contractingelectrocaloric effect material layers 202B of the heat transfer stacks104. The controller 112 may again be configured to control theapplication of this electrode control signal from the power source 110according to an operational status of the heat source 106, a temperatureof the heat source 106, a predetermined schedule, or any other desiredfactor. As described above, according to various implementations, thecontracting electrocaloric effect material layers 202B may or may not beconfigured as electrocaloric effect material segments 802 having stressrelief gaps 804 between the segments to accommodate lateral dimensionalchanges. The electrode control signal may include an oscillating signalthat can be provided as any of a variety of voltage or currentwaveforms, and may be applied substantially concurrently to theexpanding electrocaloric effect material layers 202A as described withrespect to block 1002.

According to an alternative implementation, the oscillating voltage orother signal applied across the expanding electrocaloric effect materiallayers 202A may be different than the oscillating voltage or othersignal applied across the contracting electrocaloric effect materiallayers 202B. In this embodiment, the controller 112 may determine theamplitude, frequency, or other signal characteristic to apply to therespective electrocaloric effect material layers to control the amountof expansion and contraction and control the corresponding stresses. Asan example, the transition rate, or ramp slope, and timing of theexpanding and contracting electrocaloric effect material layers202A/202B may be substantially matched. Any temporary longitudinallength change that occurs during the transition between expansion andcontraction may be transitory, occurring and correcting in less timethan the mechanical settling time of the characteristic modes of theheat transfer device 102 to minimize the stress experienced by theinterfaces between layers. This matching may include different rampslopes and timing for the expanding and contracting electrocaloriceffect material layers 202A/202B. Blocks 1002 and 1004 may be followedby block 1006.

At block 1006 (Transfer Thermal Energy While Maintaining LongitudinalLength of Heat Transfer Stack), the expanding electrocaloric effectmaterial layers 202A and the contracting electrocaloric effect materiallayers 202B react to the electrode control signal to alternatinglyactivate and deactivate, transferring thermal energy from the heatsource 106 to the heat dump 108, while the layers of thermal rectifiermaterial 204 limit the return flow of thermal energy toward the heatsource 106. According to the various embodiments described above, due tothe expansion and contraction characteristics of the electrocaloriceffect material layers and to the segmented electrocaloric effectmaterial layers with configured with stress relief gaps 804, thelongitudinal stress 310 and the lateral stress 710 are both eliminatedor mitigated during this thermal energy transfer operation. The process1000 ends when the desired thermal energy transfer operations areterminated.

FIG. 11 is a block diagram illustrating a computer hardware architecturecorresponding to an example controller 112 configured in accordance withat least some embodiments presented herein. FIG. 11 includes acontroller 112, including a processor 1110, memory 1120 and one or moredrives 1130. The controller 112 may be implemented as a conventionalcomputer system, an embedded control computer, a laptop, or a servercomputer, a mobile device, a set-top box, a kiosk, a vehicularinformation system, a mobile telephone, a customized machine, or otherhardware platform.

The drives 1130 and their associated computer storage media, providestorage of computer readable instructions, data structures, programmodules and other data for the controller 112. The drives 1130 caninclude an operating system 1140, application programs 1150, programmodules 1160, and a database 1180. The program modules 1160 may includean electric field application module 1105. The electric fieldapplication module 1105 may be adapted to execute the process 1000 forimplementing an electrocaloric effect heat transfer device 102 to reducestress induced by dimensional changes of electrocaloric effect material202 during application of an electric field as described in greaterdetail above (e.g., see previous description with respect to one or moreof FIGS. 1-10). The controller 112 further includes user input devices1190 through which a user may enter commands and data. Input devices caninclude an electronic digitizer, a microphone, a keyboard and pointingdevice, commonly referred to as a mouse, trackball or touch pad. Otherinput devices may include a joystick, game pad, satellite dish, scanner,or the like.

These and other input devices can be coupled to the processor 1110through a user input interface that is coupled to a system bus, but maybe coupled by other interface and bus structures, such as a parallelport, game port or a universal serial bus (“USB”). Computers such as thecontroller 112 may also include other peripheral output devices such asspeakers, which may be coupled through an output peripheral interface1194 or the like.

The controller 112 may operate in a networked environment using logicalconnections to one or more computers, such as a remote computer coupledto a network interface 1196. The remote computer may be a personalcomputer, a server, a router, a network PC, a peer device or othercommon network node, and can include many or all of the elementsdescribed above relative to the controller 112. Networking environmentsare commonplace in offices, enterprise-wide area networks (“WAN”), localarea networks (“LAN”), intranets, and the Internet.

When used in a LAN or WLAN networking environment, the controller 112may be coupled to the LAN through the network interface 1196 or anadapter. When used in a WAN networking environment, the controller 112typically includes a modem or other means for establishingcommunications over the WAN, such as the Internet or the network 1108.The WAN may include the Internet, the illustrated network 1108, variousother networks, or any combination thereof. It will be appreciated thatother mechanisms of establishing a communications link, ring, mesh, bus,cloud, or network between the computers may be used.

According to some embodiments, the controller 112 may be coupled to anetworking environment. The controller 112 may include one or moreinstances of a physical computer-readable storage medium or mediaassociated with the drives 1130 or other storage devices. The system busmay enable the processor 1110 to read code and/or data to/from thecomputer-readable storage media. The media may represent an apparatus inthe form of storage elements that are implemented using any suitabletechnology, including but not limited to semiconductors, magneticmaterials, optical media, electrical storage, electrochemical storage,or any other such storage technology. The media may represent componentsassociated with memory 1120, whether characterized as RAM, ROM, flash,or other types of volatile or nonvolatile memory technology. The mediamay also represent secondary storage, whether implemented as the storagedrives 1130 or otherwise. Hard drive implementations may becharacterized as solid state, or may include rotating media storingmagnetically-encoded information.

The storage media may include one or more program modules 1160. Theprogram modules 1160 may include software instructions that, when loadedinto the processor 1110 and executed, transform a general-purposecomputing system into a special-purpose computing system. As detailedthroughout this description, the program modules 1160 may providevarious tools or techniques by which the controller 112 may participatewithin the overall systems or operating environments using thecomponents, logic flows, and/or data structures discussed herein.

The processor 1110 may be constructed from any number of transistors orother circuit elements, which may individually or collectively assumeany number of states. More specifically, the processor 1110 may operateas a state machine or finite-state machine. Such a machine may betransformed to a second machine, or specific machine by loadingexecutable instructions contained within the program modules 1160. Thesecomputer-executable instructions may transform the processor 1110 byspecifying how the processor 1110 transitions between states, therebytransforming the transistors or other circuit elements constituting theprocessor 1110 from a first machine to a second machine. The states ofeither machine may also be transformed by receiving input from the oneor more user input devices 1190, the network interface 1196, otherperipherals, other interfaces, or one or more users or other actors.Either machine may also transform states, or various physicalcharacteristics of various output devices such as printers, speakers,video displays, or otherwise.

Encoding the program modules 1160 may also transform the physicalstructure of the storage media. The specific transformation of physicalstructure may depend on various factors, in different implementations ofthis description. Examples of such factors may include, but are notlimited to: the technology used to implement the storage media, whetherthe storage media are characterized as primary or secondary storage, andthe like. For example, if the storage media are implemented assemiconductor-based memory, the program modules 1160 may transform thephysical state of the semiconductor memory 1120 when the software isencoded therein. For example, the software may transform the state oftransistors, capacitors, or other discrete circuit elements constitutingthe semiconductor memory 1120.

As another example, the storage media may be implemented using magneticor optical technology such as drives 1130. In such implementations, theprogram modules 1160 may transform the physical state of magnetic oroptical media, when the software is encoded therein. Thesetransformations may include altering the magnetic characteristics ofparticular locations within given magnetic media. These transformationsmay also include altering the physical features or characteristics ofparticular locations within given optical media, to change the opticalcharacteristics of those locations. It should be appreciated thatvarious other transformations of physical media are possible withoutdeparting from the scope and spirit of the present description.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, reagents, compounds compositions or biological systems, whichcan, of course, vary. It is also to be understood that the terminologyused herein is for the purpose of describing particular embodimentsonly, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention (e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). In those instances where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember. Thus, for example, a group having 1-3 elements refers to groupshaving 1, 2, or 3 elements. Similarly, a group having 1-5 elementsrefers to groups having 1, 2, 3, 4, or 5 elements, and so forth.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. A method to transfer thermal energy from a heatsource to a heat dump, the method comprising: applying at least oneelectric field across a first electrocaloric effect material layer andacross a second electrocaloric effect material layer of a heat transferdevice in thermal contact with the heat source and the heat dump; and inresponse to the applied at least one electric field, transferringthermal energy between the first electrocaloric effect material layerand the second electrocaloric effect material layer in a direction fromthe heat source toward the heat dump while restricting thermal energytransfer in a direction from the heat dump toward the heat source and atleast partially canceling a dimensional change of the firstelectrocaloric effect material layer due to expansion by a dimensionalchange of the second electrocaloric effect material layer due tocontraction so as to maintain an approximate total length of the heattransfer device.
 2. The method of claim 1, wherein the approximate totallength of the heat transfer device corresponds to a fixed distancebetween the heat source and the heat dump.
 3. The method of claim 1,wherein applying the at least one electric field across the firstelectrocaloric effect material layer and across the secondelectrocaloric effect material layer comprises: applying an electricfield across a plurality of first electrocaloric effect material layerseffective to provide an aggregate longitudinal expansion distance thatincludes as a contribution the dimensional change of the firstelectrocaloric effect material layer due to expansion; and applying theelectric field across a plurality of second electrocaloric effectmaterial layers to provide an aggregate longitudinal contractiondistance that is substantially equivalent to the aggregate longitudinalexpansion distance, wherein the aggregate longitudinal contractiondistance includes as a contribution the dimensional change of the secondelectrocaloric effect material layer due to contraction.
 4. The methodof claim 3, wherein applying the electric field across the plurality offirst electrocaloric effect material layers and across the plurality ofsecond electrocaloric effect material layers comprises: applying a firstvoltage across the plurality of first electrocaloric effect materiallayers effective to provide the aggregate longitudinal expansiondistance; and applying a second voltage across the plurality of secondelectrocaloric effect material layers effective to provide the aggregatelongitudinal contraction distance, wherein the first voltage and thesecond voltage are determined such that the aggregate longitudinalcontraction distance is approximately equivalent to the aggregatelongitudinal expansion distance.
 5. The method of claim 4, wherein thefirst voltage is different than the second voltage.
 6. The method ofclaim 3, wherein the electric field comprises one of: an oscillatingvoltage, a pulsed signal, a pulsed direct current (DC) voltage, analternating current (AC) voltage, a ramped signal, a sawtooth signal, ora triangular signal.
 7. The method of claim 1, wherein applying the atleast one electric field across the first electrocaloric effect materiallayer and across the second electrocaloric effect material layercomprises simultaneously applying the at least one electric field acrossthe first electrocaloric effect material layer and across the secondelectrocaloric effect material layer.
 8. A method to transfer thermalenergy from a heat source to a heat dump through a heat transfer device,the method comprising: expanding a first electrocaloric effect materiallayer and contracting a second electrocaloric effect material layer ofthe heat transfer device, wherein the heat transfer device is in thermalcontact with the heat source and the heat dump; and transferring thermalenergy between the first electrocaloric effect material layer and thesecond electrocaloric effect material layer in a direction from the heatsource toward the heat dump while restricting thermal energy transfer ina direction from the heat dump toward the heat source and at leastpartially canceling expansion of the first electrocaloric effectmaterial layer by contraction of the second electrocaloric effectmaterial layer so as to maintain an approximate total length of the heattransfer device.
 9. The method of claim 8, wherein the approximate totallength of the heat transfer device corresponds to a fixed distancebetween the heat source and the heat dump.
 10. The method of claim 8,wherein: expanding the first electrocaloric effect material layercomprises applying a first electric field across the firstelectrocaloric effect material layer; and contracting the secondelectrocaloric effect material layer comprises applying a secondelectric field across the second electrocaloric effect material layer.11. The method of claim 10, wherein applying the first electric fieldacross the first electrocaloric effect material layer comprises applyingthe first electric field across a plurality of first electrocaloriceffect material layers effective to provide an aggregate longitudinalexpansion distance that includes as a contribution an expansion distanceof the first electrocaloric effect material layer.
 12. The method ofclaim 11, wherein applying the second electric field across the secondelectrocaloric effect material layer comprises applying the secondelectric field across a plurality of second electrocaloric effectmaterial layers to provide an aggregate longitudinal contractiondistance that includes as a contribution a contraction distance of thesecond electrocaloric effect material layer.
 13. The method of claim 10,wherein applying the first electric field across the firstelectrocaloric effect material layer comprises applying a first voltageacross a plurality of first electrocaloric effect material layerseffective to provide an aggregate longitudinal expansion distance thatincludes as a contribution an expansion distance of the firstelectrocaloric effect material layer.
 14. The method of claim 13,wherein: applying the second electric field across the secondelectrocaloric effect material layer comprises applying a second voltageacross a plurality of second electrocaloric effect material layerseffective to provide an aggregate longitudinal contraction distance thatincludes as a contribution a contraction distance of the secondelectrocaloric effect material layer; and the first voltage and thesecond voltage are determined such that the aggregate longitudinalcontraction distance is approximately equivalent to the aggregatelongitudinal expansion distance.
 15. The method of claim 14, whereinapplying a first value of the first voltage is not equal to applying asecond value of the second voltage.
 16. The method of claim 10, whereinapplying the first electric field or the second electric field comprisesapplying one of: an oscillating voltage, a pulsed signal, a pulseddirect current (DC) voltage, an alternating current (AC) voltage, aramped signal, a sawtooth signal, or a triangular signal.
 17. A methodto transfer heat through a heat transfer device between a heat sourceand a heat dump, the method comprising: applying a first electric fieldto a first electrocaloric effect material configured to expand and tochange temperature of the first electrocaloric effect material inresponse to application of the first electric field; applying a secondelectric field to a second electrocaloric effect material configured tocontract and to change temperature of the second electrocaloric effectmaterial in response to application of the second electric field,wherein a thermal rectifier material of the heat transfer device is inthermal contact with the first electrocaloric effect material and thesecond electrocaloric effect material; transferring thermal energy,facilitated by the thermal rectifier material, between the firstelectrocaloric effect material and the second electrocaloric effectmaterial in a direction from the heat source toward the heat dump whilemaintaining an approximate total length of the heat transfer device; andlimiting transfer of the thermal energy, facilitated by the thermalrectifier material, between the second electrocaloric effect materialand the first electrocaloric effect material.
 18. The method of claim17, wherein maintaining the approximate total length of the heattransfer device comprises maintaining a first longitudinal distanceassociated with an expansion of the first electrocaloric effect materialin response to application of the first electric field to beapproximately equivalent to a second longitudinal distance associatedwith a contraction of the second electrocaloric effect material inresponse to application of the second electric field.
 19. The method ofclaim 17, further comprising: providing a plurality of layers of thefirst electrocaloric effect material; providing a plurality of layers ofthe second electrocaloric effect material; and providing a plurality ofthermal rectifier material layers disposed between adjacent layers ofthe first and second electrocaloric effect materials.
 20. The method ofclaim 19, wherein maintaining the approximate total length of the heattransfer device comprises: expanding each of the plurality of layers ofthe first electrocaloric effect material a first longitudinal distancealong a longitudinal axis of the heat transfer device in response toapplication of the first electric field; and contracting each of theplurality of layers of the second electrocaloric effect material asecond longitudinal distance along the longitudinal axis of the heattransfer device in response to application of the second electric field.21. The method of claim 17, wherein applying the first and secondelectric fields comprise: controlling application of the first andsecond electric fields from a power source to the first and secondelectrocaloric effect materials during operation of the heat source to:control expansion of each of a plurality of layers of the firstelectrocaloric effect material a first longitudinal distance along alongitudinal axis of the heat transfer device in response to applicationof the first electric field, and control contraction of each of aplurality of layers of the second electrocaloric effect material asecond longitudinal distance along the longitudinal axis of the heattransfer device in response to the application of the second electricfield, wherein an aggregate contraction of the plurality of layers ofthe second electrocaloric effect material is approximately equivalent toan aggregate expansion of the plurality of layers of the firstelectrocaloric effect material.
 22. A heat transfer system, comprising:a heat source; a heat dump; a heat transfer device in thermal contactwith the heat source and the heat dump, the heat transfer devicecomprising: a first electrocaloric effect material layer; a secondelectrocaloric effect material layer in thermal contact with the firstelectrocaloric effect material; and a plurality of electrodes positionedto apply at least one electric field across the first and secondelectrocaloric effect material layers to transfer thermal energy betweenthe first and second electrocaloric effect material layers in adirection from the heat source toward the heat dump while thermal energytransfer in a direction from the heat dump toward the heat source isrestricted, wherein a dimensional change of the first electrocaloriceffect material layer due to expansion is at least partially cancelledby a dimensional change of the second electrocaloric effect materiallayer due to contraction so as to maintain an approximate total lengthof the heat transfer device.
 23. The heat transfer system of claim 22,wherein the heat dump is separated from the heat source by a fixeddistance and the approximate total length of the heat transfer devicecorresponds to the fixed distance.
 24. The heat transfer system of claim22, wherein: the heat source comprises an electronic component or acomputer component; and the heat dump comprises an electronics case or acomputer case.
 25. The heat transfer system of claim 22, wherein the atleast one electric field comprises a first electric field and a secondelectric field, and wherein the plurality of electrodes comprises: aplurality of first electrodes positioned to apply the first electricfield across the first electrocaloric effect material; and a pluralityof second electrodes positioned to apply the second electric fieldacross the second electrocaloric effect material; the heat transfersystem further comprising: a power source electrically coupled to theplurality of first electrodes and the plurality of second electrodes andconfigured to provide a first electrode control signal to the pluralityof first electrodes that is effective to cause the plurality of firstelectrodes to apply the first electric field and to provide a secondelectrode control signal to the plurality of second electrodes that iseffective to cause the plurality of second electrodes to apply thesecond electric field; and a controller communicatively coupled to thepower source and configured to control application of the first andsecond electrode control signals by the power source.